JPH04140636A - Manufacture of specimen for measuring equally thick interference fringe and method for observing the same - Google Patents

Abstract

PURPOSE:To prevent dust or the like from attaching to a tip of a wedge crystal to enable highly reproducible measurement by making a marking flaw parallel to a first cleavage surface and making a plurality of marking flaws to perpendicularly cut a part of a surface parallel to the cleavage surface. CONSTITUTION:After a marking flaw is made on a part of a substrate surface to create a first cleavage surface 51, a marking flaw is made in parallel to the cleavage surface 51 and a plurality of marking flaws are made on the substrate surface to perpendicularly cut a part of a surface parallel to the cleavage surface 51 to create a second cleavage surface 501. Force is applied to a position of the substrate surface corresponding to the marking flaw parallel to the cleavage surface 51 on a rear face of the substrate to divide it to create a wedge crystal sample 3. The obtained sample 3 is fixed on a predetermined position of a reinforcing ring 1 with a predetermined angle to a surface in contact with the ring 1 and perpendicular to a surface of a fixing mount having width of a half or less of the ring 1 inner diameter and predetermined height. At this time the tip of the sample 3 is fixed in the vicinity of the surface and equally thick interference fringes are observed.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Application Fields of the Invention The present invention (for example, a wedge-shaped crystal made by injecting an electron beam into the tip of a wedge-shaped crystal made of a compound semiconductor to generate interference fringes due to the intensity distribution of the electron beam) This relates to a method for preparing and observing a sample for measurement of equal-thickness interference fringes to accurately measure the steepness, composition, and compositional fluctuations of heterointerfaces in the semiconductor.a.Conventional technologyRemarkable progress in recent semiconductor crystal growth technology. This makes it possible to grow crystals at the monoatomic layer level.In particular, metal-organic vapor phase epitaxy (λ40 VPE method) and molecular beam epitaxy (MBE method) have made it possible to grow crystals at the monoatomic layer level. Although lattice structures have been fabricated and optical devices such as semiconductor lasers and photodetectors that use these superlattices in their active regions, and high-speed electronic devices such as HEMTs that utilize a single heterostructure, are being developed one after another. With these developments, it has become a problem to evaluate how steep the hetero interface is, which is the force behind the extremely thin layer having the designed composition. There is a method to accurately measure the steepness and composition distribution of heterointerfaces by injecting an electron beam into the tip of a wedge-shaped crystal and observing interference fringes due to the intensity distribution of the electron beam within the crystal. As a method for preparing samples that produces interference fringes, Hitachi's Mizuta and Kakibayashi et al. have developed an electron microscope Vol. 1.24, N
o, 1, (1989) 52. However, wedge-shaped crystals are manufactured by taking advantage of the fact that GaAs can be easily cleaved along the (110) plane.

Substrate 100 (The surface is mechanically polished from the back side of the (001) plane to a thickness of about 0.2 mm to facilitate separation (Fig. 4a).

Cleavage device (scriber 101, movable sample stage,
Scratches 102 are made in the vertical and horizontal directions using an optical microscope or the like (FIG. 4b). Next, place the knife 103 directly under the scribing scratch 102 as far as possible from the scribing scratch 102 on the part ζ to be used as a sample.
Separate the sample piece by applying a light force to both ends (Figure 4C)
. Wrap the sample pieces in paraffin paper 104 to prevent contamination, and be careful not to cause the cleaved sample pieces to collide with each other and chip the tips. Observation part 106
After confirming that there are no contamination or defects using an optical microscope, proceed to
A sample is obtained by cutting to a length of rnm (Fig. 4d).

The method for fixing the wedge-shaped sample 105 to the TEM sample holder is as follows: Since a top entry type or side entry type two-axis inclined holder is used, fixation is possible on the top gimbal 110.
A jig 112 with a groove 111 having a width of 2 mm and an inclination of 45° is installed.
If it is inserted into the groove 2 (not shown), it can be fixed at the focal position of the lens of the electron beam 113 at an angle of 45@ (Fig. 5).

Problems to be Solved by the Invention However, since the inclination angle of the sample holder in the sample prepared by the above method is limited to 45°, the angle of the tip of the wedge-shaped crystal sample 105 is 90''. For example, (fl, in the case of a GaAs sample, (110)
It can be cleaved at (110) and the tip becomes 90° (00
1) In the case of an epitaxial film on a plane, the force with which a sample for observation can be prepared by the above method (not only cannot it be applied to an epitaxial film on a (111) plane where the tip after cleavage is 60° or 1206, but also As the sample is relatively large, it requires a large sample space within the TEM device - it also requires a special holder for fixing the sample, and cannot be used in existing TEM devices with limited measurement space. When fixing the sample! If you just insert it into the 0.2mm width groove, the sample may fall inside the TEM equipment, which may cause contamination inside the TEM equipment.
As the wedge-shaped sample becomes larger, the measurement space must be enlarged, which may reduce the measurement accuracy, so it is better to make the measurement sample as small as possible. When preparing a sample in which the first cleavage plane and the second cleavage plane intersect, an electron beam is incident on the tip of a wedge-shaped crystal to observe equal-thickness interference fringes.
After making a scratch on a part of the surface of the substrate and applying force from the back side of the substrate to create the first cleavage plane, make a scratch at a predetermined position on the back side of the substrate parallel to the first cleavage plane. and make a plurality of scratches on the surface of the substrate so as to vertically cut a part of the plane parallel to the first cleavage plane, and apply force from the back side of the substrate to create a second cleavage plane. The substrate surface is divided by applying force to the position of the first cleavage plane parallel to the first cleavage plane made on the back surface of the substrate.
Provided is a method for preparing a sample for measurement of interference fringes of equal thickness, characterized by producing a wedge-shaped crystal, and the wedge-shaped sample prepared by the method is placed at a predetermined position of a reinforcing ring with a diameter of 1/2 or less of the inner diameter of the reinforcing ring. When fixing the wedge-shaped crystal at a predetermined angle to a plane perpendicular to the plane in contact with the reinforcing ring of a fixing base having a width and a predetermined height, the tip of the wedge-shaped crystal is Dust and powder generated by cleavage generally tend to adhere to the tips and surrounding areas of wedge-shaped crystals prepared by cleavage (the wedge-shaped crystals produced by the method of the present invention By making a wedge-shaped crystal, no dust or powder generated by cleavage will adhere to the tip of the wedge-shaped crystal in the measurement area, making it possible to produce a wedge-shaped crystal with good reproducibility. For example, the sample can be fixed to a fixed holder even when the sample is in a fixed holder, and the sample can be separated into a size smaller than 0.7xO, 7 mm. This invention provides a method for fixing a sample to a holder tilted at 45 degrees. For example, in the case of giGaAs, the epitaxial crystal on the (001) plane is Although it can only be applied to films, the present invention does not use the above-mentioned holder, so there is no need to limit the tip of the wedge-shaped crystal to 90° (-
Therefore, for example 4: In the case of LGaAs, when the epitaxial film on the (111) plane is separated, the tip of the wedge-shaped crystal is 60° or 120°, but it can be observed by the present invention. The present invention will be explained below using examples, and FIG. 1 is a diagram showing a method for observing a sample prepared according to the present invention.
This (for example, JEOL JEOL4000FX,
It can be used without any modification to transmission electron microscopes manufactured by Hitachi or Akashi Beam. 1 is a reinforcing ring used for normal cross-sectional TEM observation, for example, 723° manufactured by Applied Technology Research or equivalent. Track 2 is an n-type semiconductor, for example, n-GaAs, and track 3 is a sample to be measured. The n-GaAs stand 2 is used as a stand for fixing the measurement sample 3 with high precision, and is used as a sample fixing surface.
It is convenient to use the cleavage plane of the s-base 2 because it has good flatness and conductivity (-Note that the cleavage plane of the s-base 2 is not necessarily the n-GaAs base 2).
However, it is not only difficult to finish a very small non-magnetic material other than a semiconductor to the same level as the cleavage plane of a semiconductor, but it also increases the cost. 6 A semiconductor substrate such as GaAs is preferable. 4 is for observation. For the sake of brevity, we will describe in detail the method of cleaving a sample according to an embodiment of the present invention using an electron beam.
The case where a sample is a shrimp film on which an epitaxial film is crystal-grown on a (001) plane GaAs substrate is also described in FIG. 2(a).
Machine polish the back side to a thickness of about 0.2 to 0.4 mm to make it easier to cleave.At this time, it is easier to cleave if the back side is not a mirror surface (~If it is made thinner than this, cleavage will be easier. However, it becomes difficult to handle, and small particles and dust from the cleavage tend to adhere to the cleaved tip. 110) Or (110) Make one scratch 21A on the surface to expose the cleavage plane.The length of the scratch 21A is about 1 mm and shallow.
The reason for making the scratches on the front surface rather than the back surface is to perform the cleavage by applying force from the back surface to obtain a cleaved surface with good flatness.

Fig. 2(c) Place the surface with the scratch 21A facing down, for example, on the penkotsuton 22, and from the back, use flat-tipped tweezers 20 or the like to gently (push and cleave) just above the scratch 21A. At the time, the hardness of the wave-cleaved semiconductor substrate is directly transmitted to the fingertips through the bottle set 10, making it easy to adjust the force. A score 21.8 is made parallel to the cleavage plane 50 on the surface at the position where the cleavage plane 51 is obtained. Or (e) cleavage” plane “5”
Use the clean one of 0 or 51 for observation.Place the sample on the clean paper 12 with the back side facing up, as shown in Figure 2(f).
Insert a thin scribe line 21c parallel to the cleavage plane 51 (first cleavage plane) at a position about 0.7 mm away from the cleavage plane 51 to be measured, leaving about 1 nm at both ends.Insert the scribe line 21c from end to end. and the sample is separated,
Care must be taken as the powder generated when marking lines may contaminate the cleavage surface to be measured.

Figure 2 (g) With the surface of the sample facing up, make scratches 2ID every 0.7 mm from appropriate positions on the opposite side of the cleavage plane to be measured.

Figure 2 (h,) Turn the sample upside down and make scratch 2 in the same way as (b) or (e).
A rectangular parallelepiped sample 3 is made in the form of a rectangular parallelepiped by cleaving at 1D.4 The cleavage plane 500 at this time is the second cleavage plane. hand,
Press and cleave the area just above the scribing scratch 21C on the back side with a flat-tipped tweezers 20, etc. to create a sample 3 for observation and measurement. 7XO, 7 mm square measurement samples can be prepared with good reproducibility without most of the cleaved planes being chipped or contaminated by powder generated during cleavage. & Tweezers with a flat tip - wood A bottle set with a sharp tip - end 1 piece of clean paper You only need 2 sheets of penkotsuton, no special jig is required~ In the above method, Teflon is used instead of clean paper. You can also use a plate (you must be careful not to have any lumps or other adhesion). This is because the coating material of the transparent wrap may adhere to the cleaved surface of the measurement sample, or the sample may adhere to the transparent wrap after cleavage, making handling inconvenient. Next, the table (n-GaAs2) for fixing the sample 3 made of the wedge-shaped crystal produced as described above and the method for fixing it will be described in detail.

For example, as a stand 2, the surface is (OOl) plane and the thickness is 350μ.
The method for making the 4-piece 2 by cleavage using GaAs with a diameter of approximately
When using 420, 2mm x 0. 5mmxQ, 3
It is convenient to use a rectangular parallelepiped with dimensions of 5m and m.As shown in Figure 1, the n-GaAs stand 2 fabricated on the reinforcing ring 1 is fixed with adhesive 7 with the surface 5 facing upward.Measurement sample 3
At this time, the sample 3 is fixed on the cleavage surface 6 of the n-GaAs stand 2 with its tip to be measured as shown in the figure.
The substrate side is bonded so that the tip of the measurement sample 3 is aligned with the line formed by the back surface 5A and the cleavage surface 6, and the sample 3 is bonded so that the angle formed by the tip of the sample 3 is divided into two equal parts.

In the case of sample 3 with a shrimp membrane formed on the (001) surface, the angle of the tip 3A is 90°, so when bonding, the angle is 4
The force to make the angle <, In the case of a sample with a shrimp membrane formed on the (111) plane, its tip should be at 60° or 1
The angle is 20°, so when gluing, use 30° or 60°.
4 These angles can be roughly divided into two equal parts. One of the advantages of this method is that it can be adjusted within the TEM device, so the accuracy does not have to be very strict.
The purpose of using n-GaAs2 is to prevent charge-up of the measurement sample.Since the cleavage can be used, a rectangular parallelepiped with a right-angled cross section can be easily formed, and the measurement sample can be fixed on the cleavage plane, which prevents the electron beam from tilting. Since the variation in the angle is small, adjustment of the electron beam between samples is hardly required.In the method described above, the force <, n-GaAs is
Instead of the base 2, a non-magnetic conductive material may be used, or it may be integrated with the reinforcing ring. The shape does not necessarily have to be circular, and can be adapted flexibly and at an extremely low cost. The method for observing thick interference fringes will be explained using Fig. 3. However, the method for observing equal thickness interference fringes of a semiconductor formed on the i;1 (001) plane will be explained as shown in Fig. 3 (a). When set in a transmission electron microscope and irradiating the tip of the wedge-shaped crystal 3 with an electron beam 4, a diffraction pattern 26 of a plane perpendicular to the electron beam 4 appears, but the Kikuchi band from the (100) plane is at the center of the screen. Since it appears near the electron beam, it is possible to easily make the (100) plane perpendicular to the electron beam. When the image is formed, interference fringes 28 appear on the screen (Fig. 3, c).

By observing the interference fringes 28 with an appropriate magnification, it is possible to evaluate the steepness of the heterointerface at the atomic layer level (FIG. 3C). 281. The shrimp layer of sample 3 is covered with an isoatomic wafer. 29 shows its lattice image.

Effects of the Invention As described above, the present invention has made it possible to easily measure interference fringes of equal thickness.9 Therefore, it has become possible to measure even samples where the tip of the wedge-shaped crystal is at an angle other than 90°, which could not be obtained with conventional techniques. Moreover, by using the present invention, it is not limited to shrimp on a compound semiconductor substrate such as GaAs, but for example, shrimp on the C-plane of a sapphire substrate, or any other sample that can be cleaved from two directions, can be processed to the same thickness. It becomes possible to measure the steepness of a heterointerface and compositional fluctuations using interference fringes, and the present invention has significant effects.

[Brief explanation of the drawing]

FIG. 1 is a strabismus doctor showing an observation state of an embodiment of the present invention. FIG. 2 is a schematic doctor showing a sample preparation method of the present invention. FIG. 3 is a doctor showing a method of observing equal-thickness interference fringes of the present invention. The figure shows a conventional sample preparation method. Figure 5 shows a conventional fixing method.
・Measurement trial 4... Electron beam 5... Base board display 6
... Cleavage grinding 7 ... Before adhesion 8 ... Adhesion K
19...Scriber-120...Tweezers, 2
1A...Scratch 22...Penkotsuton, 15
...(100)i 26-...diffraction pattern, 2
7... (000) spot, 28... Equal thickness interference fringes Name of agent Patent attorney Akira Okaji and two others Figure 4 1:50pm Kou 2 Hesa closing diagram (α) ztA+7aX'34 Kasumi

Claims (2)

[Claims] (1) When making a sample by injecting an electron beam into the tip of a wedge-shaped crystal and observing equal-thickness interference fringes by intersecting the first cleavage plane and the second cleavage plane, a part of the substrate surface is After creating the first cleavage surface by applying force from the back surface of the substrate, a second scribe is made at a predetermined position on the back surface of the substrate parallel to the first cleavage surface. A plurality of third scratches are made on the surface of the substrate so as to vertically cut a part of the plane parallel to the first cleavage plane, and force is applied from the back side of the substrate to cut the second cleavage surface. Creating a cleavage plane and applying force to the substrate surface at a position relative to the second scribing scratch parallel to the first cleavage plane made on the back surface of the substrate to divide the substrate to produce the wedge-shaped crystal. A method for preparing a sample for measuring equal thickness interference fringes, characterized by: (2) At a predetermined position of the reinforcing ring, a fixed base having a width of 1/2 or less of the inner diameter of the reinforcing ring and a predetermined height is placed at a predetermined angle on a plane perpendicular to the plane in contact with the reinforcing ring. When fixing the wedge-shaped crystal produced by the method according to claim (1), the tip of the wedge-shaped crystal is fixed near the surface, and an electron beam is applied to the tip of the wedge-shaped crystal. A method for observing equal-thickness interference fringes characterized by irradiation.